It is known that, if required (to prevent the formation of ice or remove ice already formed), the leading edge of the nose inlet cowl of such turbine engines is deiced by heating with pressurized hot air taken from said turbine engine and conducted to said leading edge by a circuit for circulating hot air. This pressurized hot air taken from the engine is at a high temperature, for example around 500° C., such that said duct radiates heat and the surrounding structures of said nose inlet cowl that are sensitive to heat (for example the soundproofing panels made of composite material) must be protected from the heat. Furthermore, for obvious safety reasons, it is also necessary to provide protection for said surrounding structures in the event of pressurized hot air leaks or in the event of said duct being ruptured.
Accordingly, document EP-1 251 257 discloses a nose inlet cowl for a turbine engine, in particular for an aircraft, said nose inlet cowl being provided with means for deicing its leading edge and comprising to this end:                a hollow leading edge defining an annular chamber closed by a first internal bulkhead;        a pressurized hot air supply duct designed to be connected, at its rear end opposed to said leading edge, to a pressurized hot air circuit and, at its front end toward said leading edge, to an injector injecting said pressurized hot air into said annular chamber, said supply duct being at least partly arranged in a compartment defined, at the front, by said first internal bulkhead and, at the rear, by a second internal bulkhead; and        an internal protective envelope arranged in said compartment and defining an isolation volume enclosing said supply duct.        
Thus, in this known nose inlet cowl, said duct is isolated from the remaining interior space of the nose inlet cowl, and said internal protective envelope, which is continuous and integral, enables the surrounding structures to be protected from thermal radiation and pressurized hot air leaks and also from the effects of a rupturing of said duct. The provision of air inlet and outlet openings makes it possible, during normal operation, to achieve permanent internal ventilation of the isolation volume, thereby limiting the thermal radiation of the supply duct, the heat-sensitive surrounding structures thus being protected from any damage or aging associated with the exposure to high temperatures. In the event of the duct leaking, rupturing or exploding, the hot air is discharged to the outside through the outlet opening such that, once again, said surrounding structures are protected from the pressurized hot air.
This known nose inlet cowl thus perfectly performs its functions of thermally protecting said surrounding structures. However, in practice, to prevent the longitudinal expansion of said supply duct and of said protective envelope (which are generally made of steel) under the effect of the temperature from imposing stresses on said first and second bulkheads, it is required to produce each of the two elements formed by said supply duct and said protective envelope in two parts which are nested one inside the other and able to slide relative to one another in a sealed manner.
Thus, the increase due to heat in the length of said duct and of said envelope is absorbed by the retractable sliding movement of said two parts forming these elements.
However, it should be noted that the hot air circulating in said supply duct is under a high pressure, for example around 10 to 20 bar, with the result that this internal pressure has the effect of separating the two parts of said supply duct from one another during normal operation and of separating the two parts of said supply duct and the two parts of the protective envelope from one another in the event of said supply duct rupturing. This consequently results in stresses being applied to said bulkheads by the two parts of said supply duct and/or of said protective envelope, said stresses tending to deform said bulkheads by making them bulge toward the outside of the compartment. It thus becomes necessary to provide heavy and costly reinforcements designed to counter such bulging.